Buying RAM today.. Help?

Okay so I am going to my local computer store to buy RAM after work today as they have it a LOT cheaper than anywhere online at the moment.. But I can't decide which is need, the 8gb kit is £50 and 16gb kit is £80.. If I don't need the extra then I would rather save myself £30.

I mainly just have many firefox tabs open, itunes and sometimes league of legends as well as I have 2 monitors so that is on one and the rest is on another.

I hear unless I am doing video editing stuff, which I don't, then 16gb would be a waste?

8 Gb will do I think, be careful with buying RAM, Macs can be picky and it's not the first time the new RAM will have problems, Crucial seems to be the one to have the least problems, Corsair plenty.
Test the RAM ASAP after you get it inside the Mac, Apple Hardware Test can do the job, run the extended Test, to get into AHT hold D at startup.

8 Gb will do I think, be careful with buying RAM, Macs can be picky and it's not the first time the new RAM will have problems, Crucial seems to be the one to have the least problems, Corsair plenty.
Test the RAM ASAP after you get it inside the Mac, Apple Hardware Test can do the job, run the extended Test, to get into AHT hold D at startup.

If you are going to keep your Mini for a long time then I would max out the Mini and go with 16GB so you never have to think about upgrading the RAM again. You never know if the coming versions of OS X will be hungrier for memory than Mountain Lion. However future proofing is just the way I always think. Therefore as mentioned already 8GB would probably be fine for most applications today.

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